1. Field of the Invention
The present invention relates to a lighting direction control apparatus that changes the lighting direction of a lamp, such as the headlamps of a vehicle such as an automobile. The present invention relates particularly to a lighting direction control apparatus that employs a brushless motor as a drive source for a drive mechanism that changes a lighting direction.
2. Related Art
In order to ensure improved safety for an automobile in motion, a lighting direction control apparatus is provided that controls the lighting directions of headlamps, to the left and to the right, in consonance with the steering direction, and that especially when an automobile is turning a curve in a road or is cornering, directs a light axes of the headlamps forward in a direction of travel in accordance with the steering angle. For example, as shown in FIG. 1, which will be referred later in a first exemplary embodiment of the present invention, in consonance with the direction of travel control provided by a steering wheel SW in an automobile CAR, the light axes (in this case, of projector lamps 3, which are incorporated components of individual headlamps and can be horizontally deflected) of left and right headlamps LHL and RHL are horizontally deflected to control the lighting direction. When the steering angle is 0, i.e., when the automobile CAR is travelling directly forward, this lighting direction control apparatus stabilizes the headlamps so they are pointed forward in the direction of travel. When the steering angle is changed, to the left or right, the lighting direction control apparatus deflects the headlamps to the left or right in consonance with the angle change. In order for such a deflection to be performed, a sensor must be provided for each headlamp to detect a headlamp deflection angle, and the output of the sensor is used to control the deflection angle of the headlamp. However, since the structure of the control apparatus becomes complicated when the angle sensor is provided, it has been proposed that the deflection angle of the headlamp be detected by controlling the rotational angle of a motor that serves as the drive source for a headlamp deflection drive mechanism (an actuator) that is closely related to the deflection angle of the headlamp, e.g., by controlling a count value for a brushless motor. That is, when a correlation between the deflection angle of the headlamp and the count value of the brushless motor is obtained in advance, thereafter, only the count value for the brushless motor need be controlled for the deflection angle of the headlamp to be adjusted.
For the lighting direction control apparatus, a so-called initialization is required, i.e., a forward position in the direction of travel of the automobile, or a predetermined deflection angle position near this is set as the initial head lamp position, and the count value, at this time, for the brushless motor is obtained. As the basic initialization method, until rotation of the brushless motor is halted, the headlamp is deflected to the deflection limit in one direction, and this state is defined as a bumped state. While this bumped position is regarded as the initial position, the current count value for the brushless motor must be obtained.
However, during the initialization process, when the brushless motor is bumped to the bumped position in one direction, backlash occurs in a plurality of gears constituting a drive mechanism for deflecting the headlamp, or the gears in the rotational direction will be deformed. Then, an overrun may occur, i.e., although the deflection movement of the headlamp is halted, there may be a further small angular rotation of the brushless motor. Because of this overrun, an error caused by the backlash or the gear deformation will be included in the count value obtained for the brushless motor by the initialization. Thus, on initialization, the reliability is degraded, and thereafter, deflection control accuracy for the headlamp is reduced. It should be noted that overrun due to the above described backlash and overrun due to gear deformation are, for example, about 0.3° and 0.5°, when used to describe deflection angles for headlamps.
FIG. 10A is a graph showing a correlation between the count value for a brushless motor and the deflection angle of a headlamp. Assume that by rotating the brushless motor the headlamp is deflected in one direction and is bumped to the initial position (0°) for the forward travel of an automobile. The angle set for the headlight is 0°; however, due to the above described backlash and the deformation of the actuator gears, there is an overrun that is equivalent to a deflection angle, and accordingly, an error occurs. Therefore, the next time the brushless motor is rotated in the reverse direction, the error attributable to the overrun is not corrected. Further, during a period wherein the error due to the overrun is corrected, the correlation between the deflection angle of the headlamp and the count value for the brushless motor is lost, and hysteresis occurs. Thus, so long as hysteresis is present, the headlamp can not be deflected accurately.
In order to resolve the initialization error due to the overrun, a two-sided bumping method and a one-sided bumping method have been proposed. According to the two-sided bumping method, as described in JP-A-2004-106770, a headlamp is bumped to a position at which the headlamp can be deflected to the maximum angle (almost 1°) in a widthwise center direction (hereinafter referred to as the inward direction) of an automobile from the forward direction of travel of the automobile, and the current count value for the brushless motor is obtained.
Further, the headlamp is bumped to a position at which the headlamp can be deflected to the maximum angle (almost 20°) to the left and to the right (hereinafter referred to as the outward direction) of the automobile from the forward direction of travel, which is the direction the reverse of the inward direction, and the current count value for the brushless motor is also obtained. These obtained count values for the inward and outward bumped positions are employed to calculate a count value that corresponds to the initial position of the headlamp.
In this manner, the initialization is performed. By using the two-sided bumping method, since overruns at the individual bumped positions occur in directions opposite to each other, the overruns can offset each other, and the initialization errors due to the overruns can be corrected. However, using the two-sided bumping method, the operations for bumping the headlamp in both the inward direction and the outward direction are required, so that it takes time to perform the initialization.
According to the one-sided bumping method, until the rotation of a brushless motor is halted, a headlamp is deflected to the deflection limit in one direction, and is set to the bumped state. Then, in this state, the headlamp is deflected in the opposite direction and is set at the initial position, and the current count value for the brushless motor is obtained.
For example, as shown in FIG. 9, a left headlamp (projector lamp 3) is bumped to an angle position that is displaced about 1° inward from the 0° position, which is the initial position in the forward direction of travel. Then, the left headlamp in the bumped state is returned about 1° outward, and is set in the initial position. In this case, 1° is a slightly greater angle than an angle of 0.8°, which includes an overrun caused by the backlash and the gear deformation. As a result, as shown in FIG. 10B, where the correlation between the count value for a brushless motor and the deflection angle of a headlamp is shown, when the motor has overrun upon the bumping of the headlamp, the overrun is resolved by rotating the brushless motor about 1° in the opposite direction. Therefore, when in this state the headlamp is set at the initial position, a reliable initialization is enabled. Furthermore, according to the one-sided bumping method, the headlamp must be bumped to only one side, especially in the inward direction where the deflection angle is smaller than is that for the outward direction. Therefore, the period required for bumping can be reduced, and the initialization process can be shortened.
However, according to the one-sided bumping method, in order to resolve the error due to the overrun, the bumped position is set inward, about 1° from the initial position. Therefore, when the left headlamp is bumped in the inward direction during the initialization process, the left headlamp is deflected about 1° from the initial position, i.e., to the right in the forward direction of travel, and would dazzle the driver of a car approaching from the opposite direction. In order to prevent this dazzling, headlamps should be turned off during the initialization, or the light axes of the headlamps must be adjusted to the low level. The first case is not preferable because, for an automobile, the forward lighting is insufficient to ensure safety. The second case requires a device for adjusting the level, and the structure of the lighting direction control apparatus becomes complicated.